Please provide second sign that Auto Sync is on. For example, change font color or background color when developing more than one photo. Maybe change the border color of the photo or LR panel. Maybe add a large display of quantity of images that are being synced.
I agree with Eliot. There has to be a better methodology and visual indication when you are Sync-ing Settings of images in LR. The underlying code to update the DB with the synced settings wouldn't have to change, just the user interface. An indication of a "Source" and "Destination" would go a long way to improve this. heck, just outlining the source image in one color and destination image(s) in another color would be helpful and reduce guesswork.